Cell Bio Exam 2: Membrane Transport

Does a large molecule diffuse at a higher or lower rate than a small molecule?

A lower rate

What is the form of energy required to perform active transport?

ATP hydrolysis

Active transport proteins bind ATP, hydrolyze it, and the resulting change in their tertiary structure allows the transport to occur. What are these ATP-hydrolyzing proteins called?

ATPases

How does active transport help to rid the cell of excess water? Does the water go from high -> low concentration, or the reverse? Does this require energy?

Active transport helps cells that have no cell walls, such as protists, to pump water out as fast as it comes in. Water moves from low to high concentrations. This uses lots of energy.

How do cells living in salty environments protect themselves against water diffusing out of the cells?

Active transport of water into the cell and active transport of ions out

What is the only cellular transport mechanism that can move molecules from low concentration and send them to high concentration?

Active transport.

Which cells have a thick, rigid cell wall?

Bacteria, come archaeans, plant, and fungal cells

What are the ways that cells deal with osmotic water influx?

By having a thick, rigid cell wall Active transport of water out of the cell Cells bathed in isotonic body fluids

How are facilitated diffusion channels regulated by changes in membrane voltage (Voltage-gated)?

Cell membranes have an electrical voltage across them due to an imbalance of ions. The inside of the membrane is electrically negative relative to the outside. The electrical gradient (electric field) is equal to the thickness of the lipid bilayer. Very high electric field can push or pull charged amino acids, altering the protein's tertiary structure. When the membrane voltage changes, amino acids in the channel pore shift around, opening or blocking the channel.

Instead of using ATP hydrolysis, some active transport proteins utilize ____, which is another form of what kind of reaction?

Co-transport, another form of coupled reaction

Facilitated diffusion can carry molecules: into, or outside of the cell, or either?

Either into or outside of the cell. All that matters is that the transport must be from high to low concentration.

What is it called when a molecule generates a charge across the membrane? (electricity-producing)

Electrogenic

Which form of transport is the process where specific membrane proteins assist in allowing molecules that are either too large or too polar to cross the membrane?

Facilitated diffusion

Which form of transport is vital for cell uptake of nutrients, and moving critical substrates and metabolites into or out of cells or cellular compartments?

Facilitated diffusion is vital

How are facilitated diffusion channels regulated by binding of a regulatory molecule (Ligand-gated)?

Ligand is a generic term for a molecule that binds to a specific protein. (Example: insulin) Ligand-gated ion channels open (or close) in response to binding a specific molecule or ligand. Best examples: neurotransmitter receptor proteins found in the "receiving" terminals (dendrites) of nerve cells.

Many active transport proteins are regulated by binding specific small molecules, also called ____-gated, while others are regulated by _____ of the active transport protein. Very few, if any, active transport systems are ____-gated.

Ligand-gated Phosphorylation Voltage-gated

Simple diffusion occurs in: liquid, solids, gasses?

Liquids, but also occurs in gasses (farting), and in solids, though very slowly

How are facilitated diffusion channels regulated by phosphorylation?

Many facilitated diffusion proteins can be regulated by phosphorylation or de-phosphorlyation of specific amino acids. Can be used in addition to other two methods. (Voltage-gated and ligand-gated)

What is simple diffusion? Do molecules go from low concentration to high concentration, or the reverse? Are proteins needed?

Molecules moving directly across the membrane, going from high to low concentration. No proteins are needed.

Bathing cells in isotonic body fluids is done by what kind of organisms?

Most multicellular organisms

What is one of the most universal, from bacteria to humans, active transport systems? What is this often called?

Na+/K+ ATPases, often called the sodium-potassium pump, or just the sodium pump

Does facilitated diffusion use cellular energy?

No, only active transport uses cellular energy

Is simple diffusion specific? What does this mean?

No, this means that any molecule sufficiently small and/or hydrophobic can diffuse across a cell membrane, including molecules we don't want

Explain the transport of the two different molecules during co-transport.

One molecule is carried from high to low concentration (exergonic facilitated diffusion). The energy released by the facilitated diffusion is captured by the transport protein to power the transport of a different molecule from low to high concentration (endergonic active transport)

Is the cell wall permeable to water? How does a thick cell wall protect the cell from absorbing too much water and bursting?

The cell wall is permeable to water, so water still goes into the cell, but since it is encased inside a cell wall the cell cannot expand. It uses back pressure to protect itself.

How does bathing cells in isotonic body fluids help protect the cell from excess water gained from osmosis?

The cells of the organism are constantly bathed in body fluids full of ions, salts, and proteins that are isotonic: they have the same water concentration as the inside of the cells. Water concentrations are equal inside and outside the cell, so there is no net osmosis at all.

What happens when you add a drop of dye to a glass of water? What type of transport is this an example of?

The dye will slowly spread out until the dye concentration is even across the entire glass of water, even without stirring. This is a form of simple diffusion.

What is osmosis? Does it move from high to low concentration, or the reverse? What is it a form of?

The simple diffusion of water across a membrane. High -> low concentration. A form of simple diffusion.

Simple diffusion rates are strongly dependent on what?

The size of the molecule

What is the Na+/K+ ATPases transport system often called?

The sodium-potassium pump, or just the sodium pump

What is this back pressure that protects the cell from bursting called? How does it work?

This back pressure is called reverse osmosis. Water is still absorbed into the cell, but the cell wall protects it from bursting. Back pressure builds up inside the cell until the pressure forces water out of the cell as fast as osmosis brings it in.

What five things are especially important functions of molecule transport across membranes by facilitated diffusion?

Transport of ions Vital roles in nerve transmission Muscle contraction Kidney function Transport of sugars by the phloem of plants

In co-transport, the protein allows transport of what?

Two different molecules

In environments with low water concentrations, such as highly salty environments, what happens to the water in the cells?

Water diffuses out of the cells, fatally dehydrating and killing them.

What will happen to the water in the cells in a fresh water environment?

Water will diffuse into the cell by osmosis until the cell swells and bursts open

Most of the time, the channels are ____, and they only open under specific circumstances.

closed

What is one of the most common co-transport systems, used by many different cells?

The H+/K+ co-transport systems (hydrogen ion/potassium ion)

For cell membranes, simple diffusion across the lipid bilayer strongly prefers molecules that are: hydrophilic, or hydrophobic? (The membrane interior is hydrophilic, or hydrophobic?) As well as molecules that are: large or small in size?

Hydrophobic for both. Small in size

Like almost all proteins, facilitated diffusion channels are _____.

Regulated

What are the ways that facilitated diffusion channels are regulated?

Regulation by changes in membrane voltage (voltage-gated) Regulation by binding of a regulatory molecule (ligand-gated) Regulation by phosphorylation

What does co-transport require in order to function?

Requires facilitated diffusion (exergonic) of one molecule to provide the energy to perform active transport (endergonic) of a different molecule One molecule must go from high to low concentration, while the other is carried from low to high concentration

What is active transport? Low -> High concentrations, or the reverse? What does it require?

Requires the use of specific active transport membrane proteins to move molecules across the cell membrane. Molecules move from low to high concentrations, allowing cells to concentrate specific molecules or eliminate molecules they don't want. Active transport is endergonic and requires energy (usually ATP hydrolysis)

What are two ways of preserving food?

Salting food and soaking food in high sugar concentrations ("candying")

Which form of transport is merely the act of moving molecules from an area of high concentration to an area of low concentration?

Simple diffusion

Which forms of transport move molecules from high to low concentration only?

Simple diffusion and facilitated diffusion

Microelectronic chips depend on simple diffusion in: liquids, solids, or gasses?

Simple diffusion in solids

What are the three basic categories of transport across cell membranes?

Simple diffusion, Facilitated Diffusion, Active Transport

Is the movement of molecules from high to low concentrations slightly exergonic or endogenic? Does simple diffusion require cellular energy?

Slightly exergonic. It does not require energy

What is facilitated diffusion? Low -> High concentration, or the reverse? What type of molecules does this allow to cross the lipid bilayer?

Specific membrane-spanning proteins form channels across the membrane, allowing transport of molecules across the membrane. Molecules move from high to low concentration only Allows molecules that would be too large or too polar to otherwise cross the lipid bilayer

Facilitated diffusion can also carry numerous small molecules, including what five things?

Sugars Amino acids Nucleotides ATP/ADP GTP/GDP

What are two examples of highly salty environments (low water concentrations) where there is little to no life?

The Dead Sea in Palestine and The Great Salt Lake in Utah